Insulating refractories



March 30, 1965 C) Kniffe/wa 46E/vr E. EINSTEIN ETAL 3,176,054

INSULATING REFRAGTORIES Filed April 9, 1962 United States Patent O3,176,054 INSULATING REFRACTORIES Edward Einstein, Homestead, and Donald0. McCreight,

Bethel Park, Pa., assignors to Harbison-Walker Refracariaasi Patentedlidar. 3Q, i365 porous structure which is desired in a refractoryinsulation.

Accordingly, it is an object of this invention to provide an improvedrefractory insulation. Another object of the Expandable polystyrenebeads (for our use these were expanded; -10 on 20 mesh (Tyler) to adensity of 2-4 pcf.) 7.0 7. 6

Norerpandable polystyrene beads:

yvggany, Pittsburgh, Pao a corporativa f 5 invention is to provide amethod of fabricating improved refractory insulating materials. lt isstill another object Filedgfehssw of this invention to providearlightweight, porous, high i purity, alumina refractory insulationexhibiting good so- This invention relates to insulating refractoriesand lidity and handleability with incident ease of packaging moreparticularly to lightweight, porous, refractory, inand transportation.And it is yet Ianother object of this sulating materials and methods ofmanufacture therefore. invention to provide a method of fabricating alightweight,

It has been Well known and understood in the art that porous, highpurity alumina refractory insulation ma- `various combustibles can bemixed with untired refractory terial which resists expansion anddisruption on ring, material so that, after forming and tiring, a porousskelehas better strength, and which is easily made from comtal structuresuited for use as a refractory insulation will mercially available rawmaterials. result. The combustibles have included various organic In oneembodiment, a preferred method of fabricating materials, both naturallyoccurring and synthetic. D-` the insulating refractory material of thisinvention inatomaceous earth, gas developing materials and foamingcludes mixing a quantity` of -325 mesh (Tyler) high agents, ily ash,asbestos, exfoliated pyrophyllite, mica purity alumina and a quantity ofhollow, spherical, eX- and the like, have also been suggested andutilized in V panded, rigid plastic beads in a selected brickmakingforming a low density lightweight refractory insulation braded sizerange. The mixture is preferably blended material. with water to providea uniform, smooth, heavy, substan- The art is well developed in usingthe foregoing matially nonflowing cream-like material. This material isterials in combination with iireclay and the like and the placed inmolds and machine-vibrated to orient the rigid insulating products whichresulted have been satisfactory plastic beads. The molded material issubjected to a carein many installations despite problems of friability,crackfully controlled burn including an initial rapid heat to ing, andincomplete burnout of combustible materials 1700 F. The atmosphere ofthis 1700 F. heat is lean which sometimes later reacted with processexudate in in oxygen i.e. reducing, whereby the plastic beads are actualmetallurgical installations. caused to char slowly. The burn iscontinued at 3000 It has been suggested recently that one manner of in-F. until the charred beads are gasiiied without disruptions creasing thesolidity of lightweight porous reclay refracor cracking ofthe moldedmaterial. This 3000i F. burn tory insulating materials would be to usecompressible, need not `be in a non-oxidizing atmosphere. `Onalaborablown or foamed plastics. tory scale test the 3000" F. burn wasfor 5 hours. The

However, the art apparently has not recognized a methdrawing, which isin flow sheet form, delineates the foreod of successfully fabricating ahigh purity alumina regoing process in graphic form. actory insulation.The various combustibles and other Preferably, the initial 1700 F. heatis completed in materials which have been incorporated withiireclay andabout one hour, but the actual time is controlled by the the like do notappear compatible with high purity alumiquantity and rate of charring ofthe plastic beads, the na` to produce a satisfactory refractoryinsulation. For size of the molded shape, etc. The molds which are usedp the mostpart, this is because of residual inclusions which for formingthe shapes to be fired are preferably moistureare diicult to removeafter an insulating shape has been absorbent and may be such ascardboard or plaster. formed. The residual inclusions are apparently thereinsulating refractory which resulted from the foresult` of the mass ofmaterial which must be used in the going treatment steps had a thermalconductivity or K `original forming in order to obtain the low densityfactor of about 3 to 4 B.t.u./ft.2/ F. diiference for l" Table I MixNumber G 3 C 4 C 5 C 6 Mix, percent:

-325 mesh (Tyler), purity alumina.. 58.1 63. 3 p 67. 5 63. 6

60 mesh (Tyler) mesh (Tyler) Calcium Alurninate lCement 1--..

Lignin liquor 2. 6 0 6.3 6. 7 6. 4 35% solution of an organic sodiumsalt in H2O (Used as a dispersing agent)3. 1. 7 1. 9 2.0 1.9 Water 34. 038. 0 37. 0 28. 0 SS Glass, a sodium silicate of the Philadelplna QuartzCompany (slow solution) Soda/silica ratio 1/3.22 34 GD Silicate, asodium silicate of `the Philadelphia Quartz Company (last solution)Soda/silica ratio 1/2.00 i 32 Burn. 3,000 F. burn, 5 hr. hold. reducingconditions to l 700 F. Bulk Dens1ty, p.c.f 30 30 43 39 Cold CrushingStrength, p.s.i 280 180 1,050 600 1 Such as Rolandschuette, 52% alumina,less than 1% iron oxide, trace impurities the remainder analyzing SiO2and CaO on an oxide basis.

2 Waste liquor of paper industry, used as a tempering fluid.

3 Such as Darva-n #7"of the R. T. Vanderbilt Company.

' the sodium silicate additions. tional tests are set forth in Table Ilbelow:

thickness. The shapes were strong and substantially unii testing ofcomparative mixes according to the concepts f this invention.

The foregoing tests indicated the important nature of propercombinations of graded size ranges for the plastic beads. Note for.instance the relatively low strength of Mixes 3 and 4 as compared toMixes 5 and 6. Therefore, additional tests were undertaken studying theimportance of (l) a graded size range for the plastic beads and (2) Theresults of these addiprovide about 60 to 70% of the volume of the mix.The other 40 to 30% is made up of the non-expandable beads, temperinguid, the alumina and sodium silicate.

As discussed above, the initial 1700 F. tiring should be relativelyrapid. This is because of the very nely divided state of the alumina'andthe propensity of the skeletal structure, which results after charringout of the beads, to

, crumble if disturbed. However, by continuing the 1700 F. burn with`a-3000 F. burn for about five Vmore hours, the high purity aluminaskeletal structure is solidilied to producey an insulating refractory ofgood strength. The relatively high water content in'the initial mix isalso important to the successful practice of our invention.

- It is preferable to add sufficient Water to provide a quantity of freeWater in the mix for molding.- The free water is in essence .a lubricantwhich provides vfluidity to the otherwise non-owable mix. `Also, the'free water assists in allowing more uniform pa1ticle-orientation duringthe .1 Waste liquor of paper industry, used as a tempering fluid. 2 Suchas Darvan #7 of the R. T. Vanderbilt Company. 5 Cmdboard.

In the tests of Table ll, the expandable polystyrene beads were in `therange of 10 on 20 mesh (Tyler), and

' were substantially all hollow. A workable size range is mentionpolystyrene beads as beads usable'according to the concepts of thisinvention. It should be understood that other plastic materials in beadform can be utilized.

However, any selected bead material must be substantially rigid, must bein a good, graded brickmaking size range to provide the necessaryaggregate base for the very nely divided high purity alumina so that :itmay be molded and cast. The beads which are usedshould substantially allbe spherical and hollow. The spherical shape and hol- `lowness areimportant aspects of the successful practice of our invention, in that alarge surfaceV area is presented with but little weight, assuring easeof complete removal of the bead material, and to provide substantiallyuniform distribution of pores, upon tiring. As noted above, some of theVfiner beads were not hollow. These solid beads should be kept to aminimum, and in the iner size ranges to be tolerable, in order to assurecomplete removal on iiring.

In the laboratory data above, we discuss a mixture of expandable andexpanded beads. However, it should be understood that the expandablebeads, before mixing with the alumina, have been preexpanded to producea stable rigid structural entity.

The expanded beads which are substantially all hollow,

Table Il Mix Number C 7 C 8 C 9 C 10 C 11 Mix, percent:

Lightly calcined high purity 95+% A1203, -325 mesh (Tyler) 71. 0 68. 071. 0 66. 0 66 Expandable polystyrene beads (for our Y use these wereexpanded to a density of 2-4 pei.) 4.4 8.3 4.4 4.0 4 Nonexpandablepolystyrene beads 24. 6 23. 7 24.6 30. 0 30 Lignin liquor 1 7 7 7 7 7solution o1 an organic sodium salt in in H2O (Used as n dispersingagent) 2.-. V2 2 2 2 2 Water 37 0 35.6 37 34.5 34.5 GD silicate, asodium silicate of the Y Philadelphia Quartz Company (fast solution)Soda/silica ratio 1/2.00 0.07 0.07 0.07 Y old (a) (3) (3) Plaster Burn3,000" F., 5 hr. hold, reducing atmosphere to l,700 F. Bulk Density,pci.. 39 32 42 43 37 Cold Crushing Strength on Flat, p.s.l- 535 305 590640 485 vibration step 'of the molding. YHowever, we have fabricatedsatisfactory insulating lrefractory homla mixture v whichwas dried aftermixing and forming but before firing.

Having thus described-our invention in detail and-with suflicientparticularity as to enable Ythose skilled in the art to practice it,what we desire to have protected by Letters Patent is set forth in thefollowing claims.

We claim: l. That method of fabricating lightweight, porous refractoryinsulating shapes, which comprises the steps of; mixing a batch of 3ingredients, a first ingredient constituting the major portion, byweight, of said batch and being very finely divided -325 mesh alumina; asecond batch ingredient being charrable bead-like material consisting ofrelatively coarse but stable structural entities -4-l-35 mesh in size,the third batch ingredient being fine charrableV bead-like material inthe range 28+ 150 mesh, said -4-{315 mesh bead-like material constitutedfrom 60 to 70%, by volume, of the batch, the remaining 30 to 40%, byvolume, of the batch being the -28-1-150 mesh bead material and thealumina, adding suiiicient tempering liquid to the batch to provide aformable mixture, forming the resulting mixture into shapes, subjectingthe shapes to an initial burn in a non-oxidizing atmosphere to atemperature of about 1700 F. to char the bead-like material, and then toa subsequent burn at a higher temperature for a time sufficient togasify and remove all of the bead-like material Without disruption andcracking of the shapes.

2. That method of fabricating lightweight, porous refractory insulatingshapes, which comprises the steps of;

mixing a batch of 3 ingredients, a first ingredient con- `mesh in size,the third batch ingredient being tine charrable bead-like material inthe range 284-150 mesh,

Y said 44-35 mesh bead-like material constituted from 60 to 70%, byvolume, of the batch, the remaining 30 to 40%, by volume, of the batchbeing the 284-150 mesh bead material and the alumina, the aluminaconstituting 60 to 70%, by Weight, of the batch, adding sufficienttempering liquid to the batch to provide a formable mixture, forming theresulting mixture into shapes, subjecting the shapes to an initial burnin a non-oxidizing atmosphere to char the bead-like material, and thento a subsequent burn at a higher temperature for a time suiicient togasiiy and remove all of the bead-like material without rable bead-likematerial in :the range 284-150 mesh,

said 44-35 mesh bead-like material constituted from 60 to 70%, byvolume, of the batch, the remaining 30 to 40%, by volume, of the batchbeing the 284-150 mesh bead material and the alumina, the aluminaconstituting 60 to 70%, by weight, of the batch, adding 0 to 1%, byWeight, of a Water soluble sodium silicate, adding sucient temperingliquid to the batch to provide a formable mixture, forming the resultingmixture into shapes, subjecting the shapes to an initial burn in anon-oxidizing atmosphere -to char the bead-like material, `and then to asubsequent burn at a higher temperature for a time suicient to gasifyand remove all of the bead-like material Without disruption and crackingof the shapes.

4. That method of fabricating lightweight, porous refractory insulatingshapes, which comprises thesteps of; mixing a batch of 3 ingredients, arst ingredient constituting the major portion, by Weight, of said batchand being very finely divided refractory material; a second` batchingredient being charrable bead-like material consisting of relativelycoarse but stable structural entities 44-35 mesh in size, the thirdbatch ingredient being line -charr-able bead-like material in the range284-150 mesh, said 44-35 mesh bead-like material constituted from to70%, by volume, of the batch, the remaining 30 to 40%, by volume, ofthebatch being the 284-150 mesh bead material and the refractory, addingsuilicient tempering liquid to the batch to provide a formable mixture,forming the resulting mixture into shapes, subjecting the shapes to aninitial burn in a non-oxidizing atmosphere to char the bead-likematerial, and then to a subsevquent burn at a higher temperature for :atime suliicient to gasify and remove yall of the bead-like materialwithout disruption and cracking of the shapes.

References Cited by the Examiner UNITED STATES PATENTS 350,921 10/86Dudley 106-65 2,242,434 6/41 Norton 25-156 Y 2,251,687 8/41 Norton25-156 2,360,929 10/44 Blaha. 2,399,225 4/46 Heany 106-65 2,996,389 8/61Fernhof 106-71 FOREIGN PATENTS 1,126,302 3/62 Germany.

`ROBERT F. WHITE, Primary Examiner.

MORRIS LIEBMAN, ALEXANDER H. BRODMER- KEL, Examiners.

1. THAT METHOD OF FABRICATING LIGHTWEIGHT, POROUS REFRACTORY INSULATING SHAPES, WHICH COMPRISES THE STEPS OF; MIXING A BATCH OF 3 INGREDIENTS, A FIRST INGREDIENT CONSTITUTING THE MAJOR PORTION, BY WEIGHT, OF SAID BATCH AND BEING VERY FINELY DIVIDED -325 MESH ALUMINA; A SECOND BATCH INGREDIENT BEING CHARRABLE BEAD-LIKE MATERIAL CONSISTING OF RELATIVELY COARSE BUT STABLE STRUCTURAL ENTITIES -4+35 MESH IN SIZE, THE THIRD BATCH INGREDIENT BEING FINE CHARRABLE BEAD-LIKE MATERIAL IN THE RANGE -28+150 MESH, SAID -4+35 MESH BEAD-LIKE MATERIAL CONSTITUTED FROM 60 TO 70%, BY VOLUME, OF THE BATCH, THE REMAINING 30 TO 